// needed and is a bit unwieldy. The precise form is
//
//	actionID/[.../]contentID
//
// where the actionID and contentID are prepared by buildid.HashToString below.
// and are found by looking for the first or last slash.
// Usually the buildID is simply actionID/contentID, but see below for an
// exception.
//
// The build ID serves two primary purposes.
//

func (a *Action) BuildActionID() string { return actionID(a.buildID) }

// BuildContentID returns the content ID section of a's build ID.
func (a *Action) BuildContentID() string { return contentID(a.buildID) }

// BuildID returns a's build ID.
func (a *Action) BuildID() string { return a.buildID }

// BuiltTarget returns the actual file that was built. This differs
// from Target when the result was cached.

	f, err := os.Open(file)
	if err != nil {
		log.Fatal(err)
	}
	matches, hash, err := buildid.FindAndHash(f, id, 0)
	f.Close()
	if err != nil {
		log.Fatal(err)
	}

	// <= go 1.7 doesn't embed the contentID or actionID, so no slash is present
	if !strings.Contains(id, "/") {
		log.Fatalf("%s: build ID is a legacy format...binary too old for this tool", file)
	}

			fmt.Fprintf(h, "packagefile %s=%s\n", p1.ImportPath, contentID(b.buildID(a1.built)))
			if p1.Shlib != "" {
				fmt.Fprintf(h, "packageshlib %s=%s\n", p1.ImportPath, contentID(b.buildID(p1.Shlib)))
			}
		}
	}
	// Files named on command line are special.
	for _, a1 := range a.Deps[0].Deps {
		p1 := a1.Package
		fmt.Fprintf(h, "top %s=%s\n", p1.ImportPath, contentID(b.buildID(a1.built)))
	}

	return h.Sum()